Field of the Invention
The present invention relates to an electronic device and a method of controlling the same.
Description of the Related Art
As electronic devices, touch detection devices such as touch panels are known. The touch detection device can be operated intuitively, and is thus mounted on smart phones, digital video cameras, digital still cameras, and other apparatus. In the touch detection device, a capacitive system is often employed as a detection system.
The capacitive system refers to a system of carrying out touch detection by arranging a plurality of electrodes arrayed in columns and a plurality of electrodes arrayed in rows on a touch panel surface so as to intersect with each other, and measuring a capacitance generated between the electrodes. Further, the capacitive system includes touch detection through measurement of a mutual capacitance and touch detection through measurement of a self-capacitance.
The measurement of the mutual capacitance refers to the following method. A drive pulse is applied to one of the electrodes arranged to intersect with each other, and a current change amount of the other electrode when a conductive object such as a finger is brought into contact is measured as a capacitance change amount, to thereby detect the touch. In the measurement of the mutual capacitance, the capacitance change amount per electrode when the capacitance change amount is measured is minute. Therefore, in general, the touch is detected based on the capacitance change amount obtained by integration of a predetermined number of times.
The measurement of the self-capacitance refers to the following method. One of the electrodes arranged to intersect with each other is fixed to have a predetermined potential, and a drive pulse is applied to the other electrode. A current change amount of the electrode on the drive pulse application side when a conductive object such as a finger is brought into contact is measured as a capacitance change amount, to thereby detect the touch.
In the measurement of the mutual capacitance, the capacitance change value at an intersection where the electrodes intersect with each other is measured. In the measurement of the self-capacitance, the paired capacitance change values of the one electrode and the other electrode are measured. Therefore, the touch detection through the measurement of the self-capacitance has a feature of increase in detection sensitivity, and the touch detection through the measurement of the mutual capacitance has a feature of increase in detection position accuracy.
However, in any measurement method, the capacitance change is measured based on the current integration amount obtained when the drive pulse is applied to each electrode, and the charges obtained through current integration are reset for each scan, which causes a problem in that useless power is consumed. In particular, the number of electrodes has been increased due to increase in size of the touch panel, and hence power consumption is further increased.
To address such a problem, in Japanese Patent Application Laid-Open No. 2009-116849, there is disclosed an input device in which a resistive input portion is set to a stand-by state of not carrying out input detection until contact to a capacitive input portion is detected, and is shifted to an operating state of carrying out input detection in response to the contact to the capacitive input portion.
However, the input device of Japanese Patent Application Laid-Open No. 2009-116849 requires electrode structures of the resistive input portion and the capacitive input portion, which leads to a complex structure to increase the cost. Further, the transmittance of the touch panel is reduced.